With the technical development in recent years, especially after Waste Electrical and Electronic Equipment Directive and the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment were implemented by European Union on Jul. 1, 2006, halogen-free flame-retardant laminates for printed circuits become main laminates in the market. In order to achieve halogen-free of laminates for printed circuits, the compounds containing dihydrobenzoxazine ring, and phosphorous-containing compounds may be used to achieve phosphorous-nitrogen synergistic flame retardancy. The laminates for printed circuits prepared by using benzoxazines have lower water absorption, excellent heat resistance and higher reliability, so as to occupy a certain market scale. However, benzoxazine resin has a higher hardness after curing, and a higher fragility than epoxy resin, so as to readily result in more drill abrasion and more processing difficulties when the laminates are processed. Correspondingly, toughening modification of benzoxazines becomes a research key point in the art.
One of the common methods for toughening is to add thermoplastic resins as modifying toughening agent, e.g. blending polyaryletherketone and polyarylethersulfone thermoplastic resins with benzoxazines and modifying. Such method can effectively form phase separation structure, reduce the expansion of cracks inside the material, and absorb the impact energy suffered by the material. Another method is to add rubber for toughening, e.g. amino-terminated butyronitrile rubber (ATBN), carboxyl-terminated butyronitrile rubber (CTBN) and other core-shell rubbers. Such method can also effectively absorb the impact energy suffered by the material, and increase the elongation at break. However, the laminates made by the modified benzoxazines with said methods all have a reduced glass transmission temperature, a greatly reduced and unstable heat resistance, and a sharply reduced humidity resistance. Due to the complicated system structure, the Anti-CAF cannot be ensured.
In conclusion, it is important to effectively modify benzoxazine resins used in the laminates for printed circuits, and to improve the toughness of the material while ensuring the heat resistance and glass transmission temperature. CN102850545A mentions preparing blended resins having high toughness and heat resistance by melt-blending/solution blending trimethyl hexamethylene bismaleimide resin with benzoxazine resin. However, there are more side chains in the bismaleimide resin structure, and the resin mixture cannot form specific phases unless in specific ratio. For such phases, phase separation readily takes place after these two resins are blended with other components during actual applications, which severely restricts the application prospect thereof in the electronic industry.
CN102134375 provides a halogen-free high Tg resin composition, and prepregs and laminates prepared therefrom. Although the resin composition provided therein has a high Tg, a low water absorption, low CET and better dielectric properties, it has a worse toughness and is difficult for mechanical processing, so that the industrialization thereof cannot be achieved.
CN102977551A provides a halogen-free resin composition, and a process for preparing copper-clad laminates by using the same. The halogen-free resin composition provided therein has excellent heat resistance and better processability, but the toughness thereof is worse and need to be further improved.
Therefore, it is required in the art to develop a halogen-free resin composition having excellent comprehensive properties, wherein the halogen-free resin composition shall have high glass transmission temperature, high reliability, inflaming retarding, dip soldering resistance, chemical resistance, low water absorption, lower dielectric dissipation factor, but have a lower brittleness and a higher toughness at the same time.